The three most important elements after gastric bypass surgery are to meet your daily Protein, Fluid and Vitamin requirements. food is secondary because your body is converting your stored fat into the energy that drives your body. Thus you lose weight.
Be willing to experiment. After surgery, my taste buds changed dramatically. Even Water changed. In the hospital it tasted excessively chlorinated and I could not drink it. So I experimented. sugar free popsicles became my best friend. Some individuals find hot or cold can help with fluids. For me, I found that I could tolerate flavored water. So I began using Crystal Light. I also found a new drink Bai which I liked cold. In the winter, I found that I tolerate Hot drinks such as piping hot cocoa. But you have to use the "No Sugar Added" variety. Also fine English teas were very good. Your fluid requirement can also be met by the water component of Soups and by the water/milk use in making your Protein shakes.
What concerns me about your thread, is that you indicated that whenever you drink, you experience pain. This is not normal. Pain is normally an indicator that your body feels something is wrong. Therefore this issue should be discussed with your surgeon's office.